402 Mr. 0. H. Latter on the secretion of 
(v.) The origin of the potassium secretion. 
It will be best to trace the develop raental changes 
which occur in the alimentary canal from the first days 
of pupal life up to the emergence of the imago, though 
the reverse order of proceeding was followed in the 
actual investigations, which extended over two summers. 
The digestive tract of a freshly formed pupa consists (Fig. 
1) of a moderately long narrow oesophagus, followed by a 
long sacculated chylific stomach (mesenteron) with 
sacculated walls and of considerable width ; this is 
succeeded by a straight narrow rectum, which is about 
half the length of the oesophagus. At the point of 
junction of the oesophagus and mesenteron there lies 
a dehcate indicator. The burette was then filled with sulphuric 
acid of half -standard strength, i.e., 24'5 grammes of SO4 to 
1000 c.c. of water ; the dilute acid was then added drop by drop 
until the rosy-pink colour was just distinguishable. In the first 
experiment 0*6 c.c. of secretion was used : it required 0*32 c.c. of 
the dilute acid to produce the neutral condition (the second 
decimal place was estimated by the eye aided with a lens). Then 
the actual weight, a?, of acid may be calculated thus — 
1000 c.c. : 0-32 c.c. : : 24'5 gr. : £c gr. 
X = 'OOTS gramme. 
and taking the combining weights of the elements concerned as 
follows, viz., Hydrogen 1, Oxygen 16, Potassium 39, Sulphur 32 
since 2 (KHO) neutralise SO4 
2 (39 + 1 -f 16) 2-1-32 + 64 
112 98 
i.e., 98 grammes of sulphuric acid neutralise 112 grammes of potas- 
sium hydroxide, hence the weight, y, of potassium hydroxide 
present in the secretion can be found from the following state- 
ment — 
98 : -0078 : : 112 : y. 
.'. y = *0089 gramme 
.•. 0*0089 gramme of KHO were present in 0*6 c.c. of 
secreted fluid 
.-. in 100 c.c. of secreted fluid there would be 1.47 
grammes of KHO. 
In the second experiment 0*4 c.c. of secretion was taken and 
dealt with in precisely the same way. It required 0*2 c.c. of the 
dilute acid to produce the neutral condition in this case. Arguing 
as before, this gives 0*0056 gramme of KHO present in 0*4 c.c. of 
secretion, which, expressed in percentages, is 1*40 grammes of 
potassium hydroxide in every 100 c.c. of secreted liquid. 
